1. Field of the Invention
The present invention relates to a method and system for controlling a talk time for a PoC user, capable of freely making use of the talk time according to the priority of a talker when the talker obtains a floor without other requesters of the floor during PoC communication.
2. Description of the Related Art
Due to significant developments in mobile communication technology and extension of mobile communication networks, various extra services and applications which use a cellular phone are being provided. At the same time, demand among cellular phone users for various extra services, such as a location service, a multimedia service, and a push-to-talk (PTT) service, is increasing. Among these extra services, the PTT service supports various supplementary functions such as an instant messenger function and a status display function, as well as a group call and a voice call which are also provided by an existing radio or a trunk radio system (TRS).
Currently, standardization of a push-to-talk-over-cellular (PoC) service which employs the PTT function in a mobile communication network is actively being developed. One unique feature of the PoC service is that a user can participate in a plurality of PoC sessions and can move among the PoC sessions to use a call service. A requirement that the user can move among the plurality of PoC sessions to use the call service is specified in the Open Mobile Alliance (OMA) which is a forum for specifying mobile communications services.
FIG. 1 is a schematic diagram of a conventional PoC service system. Referring to FIG. 1, a PoC client 10, which is a service requester installed in a mobile station, is connected to a Session Initiation Protocol/Internet Protocol (SIP/IP) core network 30 which supports SIP and IP multimedia functions via an access network 20.
The PoC client 10 resides in a PoC user terminal to provide access to the PoC service. The PoC client 10 mainly serves to initiate a PoC session, participate in a PoC session that is currently proceeding, and terminate a PoC session. In addition, the PoC client 10 acts to make and transfer a talk burst, support an instant personal alert, and perform authentication when accessing the PoC service. Hereinafter, unless otherwise stated, the PoC client 10 is assumed to be the same as a PTT service subscriber.
The SIP/IP core network 30 is connected to a PoC server 60, a group list management system (GLMS) 50, and a presence server 70 in order to support the PoC service.
The PoC server 60 has a controlling PoC function for maintaining and managing a PoC session, or a participating PoC function for participating in a PoC session for a one-to-one PoC call or a one-to-many PoC call (or group PoC call).
Functional blocks of the PoC server 60 will be explained below with reference to FIG. 2.
A function of the PoC server is classified into a controlling PoC function (CF) for maintaining and managing a PoC session in general and a participating PoC function (PF) for maintaining each PoC session, which will be explained below.
TABLE 1Controlling PoC Function (CF)Provides centralized PoC session handlingProvides centralized Media distributionProvides centralized Talk Burst Arbitration functionality including talkeridentificationProvides SIP session handling, such as SIP session origination,termination, etc.Provides policy enforcement for participation in group sessionsProvides participant informationCollects and provides centralized media quality informationProvides centralized charging reportsMay provide transcoding between different codecsSupports Talk Burst Control Protocol Negotiation
As shown in Table 1, the CF serves to maintain and manage a PoC session in general. The PoC server receives requests for a floor (right to talk) from PoC clients, arranges an order in which to give the clients the floor, and gives the clients the floor in that order. The PoC server also distributes a talk burst from a specific PoC client to all PoC clients participating in a group PoC call, and provides information of the PoC clients participating in the group PoC call.
As shown in Table 2 below, the PF manages a PoC session between the CF and each PoC client. In particular, the PF acts to relay the floor between the PoC client and the CF when the PoC client requests the floor or when the CF gives the floor to the PoC client. In addition, the PF serves to relay media between the CF and the PoC client, provide transcoding between different codecs, and provide a filtering function for filtering one of two PoC sessions chosen by a user when there is simultaneous talking in two simultaneous PoC sessions.
TABLE 2Participating PoC Function (PF)Provides PoC session handlingMay provide the Media relay function between PoC Client and ControllingPoC serverMay provide user media adaptation proceduresMay provide the Talk Burst control message relay function betweenPoC Client and Controlling PoC serverProvides SIP session handling, such as SIP session origination,termination, etc; on behalf of the represented PoC Client.Provides policy enforcement for incoming PoC session (e.g. accesscontrol, incoming PoC session barring, availability status, etc.)May collect and provide media quality informationProvides the participant charging reportsMay provide filtering of the media streams in the case of simultaneoussessionsMay provide transcoding between different codecsMay support Talk Burst Control Protocol NegotiationStores the current Answer Mode and Incoming PoC Session Barringpreferences of the PoC Client
In the PoC service system described above, a PoC user can input information about a group and group members to the GLMS 50 through his/her PoC terminal, and can be aware of information about PoC users who he or she can call through an individual or group list transmitted from the GLMS 50. Alternatively, information about a group and group members in the GLMS 50 may be input, corrected and managed via a reliable communication network such as the Internet or Intranet which a PoC service provider can trust.
In order to make use of the PoC service, the PoC user registers his/her PoC address in the SIP/IP core network 30. The SIP/IP core network 30 stores PoC user information at the request of the PoC user. Thus, when another PoC user tries to request a group PoC call, the PoC user registers his/her information in the SIP/IP core network 30 in advance as described above, and requests the group PoC call to his/her SIP/IP core network by using group identification information transmitted from the GLMS 50. The SIP/IP core network 30 performs address determination and domain location determination using information of the call requesting PoC user and then transfers a PoC call request to a home PoC server with which the call requesting PoC user is registered. In regard to the PoC call request, the PoC server prepares for establishment of a PoC session, obtains each user's information from the GLMS 50, and then transfers a PoC call request signal to a corresponding SIP/IP core network 30. Here, in the case of a PoC call request to users within an Intradomain, the PoC server performs both the CF and PF. The PoC server, which manages a call-requested PoC user, requests a PoC call to the PoC user after the SIP/IP core network 30 performs the location determination procedure, by using information of the PoC user that is transmitted to the PoC server.
Referring to FIG. 3, PoC clients 111, 121, 131 and 141 provide access to a CF 100 through PFs 110, 120, 130 and 140 respectively, thereby establishing a PoC session. Here, when a floor is given to a requester qualified as a talker from the CF 100, media based on a talk of the corresponding PoC client is transmitted to each PoC client.
FIG. 4A is a flowchart showing a conventional procedure where a PoC user obtains a floor. Referring to FIG. 4A, in order to obtain a floor, a PoC client A 111 presses a PoC talk button installed to its own PoC terminal when no PoC client is talking within a PoC session where the PoC client A 111 is connected to a PoC client B 121.
Therefore, the PoC client A 111 transmits a message making a request for the floor to a PF A 110 acting as Participating PoC Function (S101), and thus the PF A 110 receiving the Floor Request message transmits the Floor Request message to a CF 100, a PoC server, acting as Controlling PoC Function of this PoC session (S101).
After receiving the floor request message, the CF 100 transmits a message, notifying that the floor is granted, to the PoC client A 111 (S102) as well as a message, notifying that the floor has been granted to the PoC client A 111, to the PoC client B 121. Since the latter message includes an identifier (ID) of the PoC client A 111 as a talker, the PoC client B 121 knows who the talker is.
Thereafter, a media session is initiated, and a talk burst is transmitted from the PoC client A 111 to the PoC client B 121 (S104).
The foregoing description is directed to the procedure of making a request for the floor when the PoC session is established. When the PoC session is not established, the PoC client A 111 makes a request to the PoC client B 121 to set up the PoC session, and the PoC server acting as the Controlling PoC Function between the two clients transmits a message relating to opening of the PoC session to the PoC client B 121. Then, the PoC client B 121 transmits a compliance response of the request to the CF 100 of the PoC server acting as the Controlling PoC Function, and the CF 100 transmits the Floor Grant message to the PoC client A 111. In this manner, the PoC client A 111 obtaining the floor transfers a talk (a data file converted into a voice signal) through the opened media session when initiating a talk with its PoC talk button pressed.
FIG. 4B is a flowchart showing a conventional procedure where a PoC user terminates a talk.
In FIG. 4B, during transferring a talk burst, the PoC client A 111 releases a PoC talk button after terminating a talk, and then the PoC client A 111 transfers a packet where the last talk of the talker is converted into a voice signal (S105) as well as a Talk Burst Complete message notifying that the talk is terminated to a CF 100 (S106). The CF 100 receiving the Talk Burst Complete message transmits a No Talk Burst message notifying that there is no talker within the session to the PoC client A 111 and PoC client B 121 (S107). Now, the session enters an idle state again.
The PoC user getting the messages in the foregoing way observes a maximum talk time period that is set up by a session establisher or a service provider. The PoC user may or not receive an indication notifying that termination of the talk is coming before the maximum talk time period has expired on the basis of a PoC service. If the talker continues to talk in spite of the expiration of the maximum talk time period, the CF does not transmit the talk burst data received from the PoC client A 111 to the PoC client B 121, which automatically results in depriving the PoC client A 111 of the floor.
In the conventional procedure, only when obtaining the floor in the PoC communication, the talker can talk for a predetermined maximum talk time period according to the setup of the provider or the PoC terminal. The standard formulated by the OMA defines the maximum talk time period so that it can be determined by the service provider or the first PoC user who establishes the session. This is because the PoC service is provided in a half-duplex mode. Specifically, if any participant of the PoC session continues to talk, the other participants cannot talk. Thus, the standard is directed to arbitrate this situation for the PoC system.
In other words, when the PoC user fails to terminate the talk for the maximum talk time period, the PoC user can make a request to the PoC server, the CF, acting as the Controlling PoC Function for the floor again after the maximum talk time period has lapsed, receive the Floor Grant message, and have the talk again, as discussed above. The PoC user has to wait for a time which it takes to obtain the floor again in the middle of the talk. Thereby, the PoC user can continue to talk, and the participants of the same session can listen to the talker (the PoC user), after they must also wait for the time which the talker requires to obtain the floor. This is also true of any talker having a priority.
However, if the floor is used in the above-mentioned way, an available time for the floor comes to an end in the middle of the talk when a person intends to continue to talk in excess of the maximum talk time period. As such, the person must stand the inconvenience that he/she performs the procedure of obtaining the floor again, and thus has the talk after obtaining the floor.